3 register controlling clock generator – NEC switch User Manual
Page 74
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CHAPTER 5 CLOCK GENERATOR
User’s Manual U12978EJ3V0UD
74
5.3 Register Controlling Clock Generator
The clock generator is controlled by the following register.
• Processor clock control register (PCC)
(1) Processor clock control register (PCC)
PCC selects the CPU clock and sets the of division ratio.
PCC is set with a 1-bit or 8-bit memory manipulation instruction.
RESET input sets the PCC to 02H.
Figure 5-2. Format of Processor Clock Control Register
CPU clock (f
CPU
) selection
0
0
0
0
0
0
PCC1
0
PCC
Symbol
Address
After reset
R/W
FFFBH
02H
R/W
7
6
5
4
3
2
1
0
PCC1
0
1
f
X
f
X
/2
2
µ
µ
Minimum instruction execution time: 2/f
CPU
0.33 s
1.33 s
f
X
= 6.0 MHz operation
Caution
Bits 0 and 2 to 7 must be set to 0.
Remark
f
X
: system clock oscillation frequency
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